[PATCH 6.4 231/800] Input: cyttsp4_core - change del_timer_sync() to timer_shutdown_sync()

Greg Kroah-Hartman
2023-07-16T20:03:38Z

From: Duoming Zhou <duoming@zju.edu.cn>

[ Upstream commit dbe836576f12743a7d2d170ad4ad4fd324c4d47a ]

The watchdog_timer can schedule tx_timeout_task and watchdog_work
can also arm watchdog_timer. The process is shown below:

----------- timer schedules work ------------
cyttsp4_watchdog_timer() //timer handler
schedule_work(&cd->watchdog_work)

----------- work arms timer ------------
cyttsp4_watchdog_work() //workqueue callback function
cyttsp4_start_wd_timer()
mod_timer(&cd->watchdog_timer, ...)

Although del_timer_sync() and cancel_work_sync() are called in
cyttsp4_remove(), the timer and workqueue could still be rearmed.
As a result, the possible use after free bugs could happen. The
process is shown below:

(cleanup routine) | (timer and workqueue routine)
cyttsp4_remove() | cyttsp4_watchdog_timer() //timer
cyttsp4_stop_wd_timer() | schedule_work()
del_timer_sync() |
| cyttsp4_watchdog_work() //worker
| cyttsp4_start_wd_timer()
| mod_timer()
cancel_work_sync() |
| cyttsp4_watchdog_timer() //timer
| schedule_work()
del_timer_sync() |
kfree(cd) //FREE |
| cyttsp4_watchdog_work() // reschedule!
| cd-> //USE

This patch changes del_timer_sync() to timer_shutdown_sync(),
which could prevent rearming of the timer from the workqueue.

Fixes: 17fb1563d69b ("Input: cyttsp4 - add core driver for Cypress TMA4XX touchscreen devices")
Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
Link: https://lore.kernel.org/r/20230421082919.8471-1-duoming@zju.edu.cn
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/input/touchscreen/cyttsp4_core.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/input/touchscreen/cyttsp4_core.c b/drivers/input/touchscreen/cyttsp4_core.c
index 0cd6f626adec5..7cb26929dc732 100644
--- a/drivers/input/touchscreen/cyttsp4_core.c
+++ b/drivers/input/touchscreen/cyttsp4_core.c
@@ -1263,9 +1263,8 @@ static void cyttsp4_stop_wd_timer(struct cyttsp4 *cd)
* Ensure we wait until the watchdog timer
* running on a different CPU finishes
*/
- del_timer_sync(&cd->watchdog_timer);
+ timer_shutdown_sync(&cd->watchdog_timer);
cancel_work_sync(&cd->watchdog_work);
- del_timer_sync(&cd->watchdog_timer);
}

static void cyttsp4_watchdog_timer(struct timer_list *t)
--
2.39.2